Optical coherence tomography (OCT) utilizing multi-wavelength light wave interference may obtain a tomographic image of a sample (particularly, a fundus) with high resolution. In recent years, in OCT apparatuses for ophthalmology, obtainment of a functional OCT image obtained by imaging optical characteristics, movements, and the like of fundus tissues is attempted in addition to a normal OCT image obtained by imaging shapes of fundus tissues.
Polarization sensitive OCT which is one of such functional OCTs performs imaging using a polarization parameter (retardation and orientation) which is one of the optical characteristics of fundus tissues. The polarization sensitive OCT may form a polarization sensitive OCT image using the polarization parameter and perform detection and segmentation of fundus tissues. The polarization sensitive OCT divides interfering light into two linearly-polarized light beams which are orthogonal to each other and detects the linearly-polarized light beams using light modulated into circularly-polarized light as measurement light used to observe a sample so as to generate a polarization sensitive OCT image (refer to PTL 1).
Furthermore, in NPL1, depolarized regions extracted from a polarization sensitive OCT image are classified into an RPE region and a choroid region. Here, “depolarization” is an index representing a degree of cancellation of polarization in a subject. The depolarization is seen to be caused by random changing of a direction and a phase of polarization due to reflection of measurement light in fine structures (melanin, for example) in tissues, for example. First, a depolarized region is extracted from a polarization sensitive OCT image, and a curve of an RPE region is estimated in the extracted depolarized region. Then a portion which is positioned far from the estimated curve to a deep side or a shallow side in a depth direction is discriminated (classified) as a choroid region. Here, according to NPL1, different colors are used for displaying the RPE region and the choroid region in the polarization sensitive OCT image.